Note: Descriptions are shown in the official language in which they were submitted.
~065~775
The present invention relates to internal shoe
drum brakes.
In accordance with the present invention, there i9
provided an internal shoe drum brake comprising: first
and second brake shoes having adjacent ends; shoe return
spring means for biasing said first and second brake
shoes toward each other; an actuator engaging one pair
of said adjacent ends of the brake shoes; mechanically
operated brake having an operating lever
having an arm carrying
a supporting pin, said arm of said operating lever being
positioned for operative engagement with said first brake
shoe; a length adjustable str~t having a tubular part
having one end in operative engagement with said second
brake shoe and a threaded part pivotally
mounted on the supporting pin and received in the tubular
part; a pawl arm pivotally mounted on the supporting
p~n an~ carrying a pawl; a ratchet wheel rotatably ;~
mo~nted on the strut on the threaded part and engaged
by the pawl for effecting adjustment of the strut length;
and biasing means for biasing the pawl into engagement
with the ratchet wheel and for biasing the pawl arm in
one rotational direction about the supporting pin
toward a predetermined angular position relative to
the supporting pin, the adjustable strut comprising
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a stopper formed on the threaded part to limit movement of
the ratchet wheel to define the minimum strut length. Further-
more the aforesaid biasing means comprise a compression coil
spring mounted around the supporting pin and having one end
anchored to a flange secured to one end of the supporting pin
and the other end engaging the pawl and a shoulder formed on
the arm of the operating lever. One form of vehicle wheel
internal shoe bra~e _
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in accordance with the present invention will now be
described, by way of example, with reference to the
accompanying drawings, in which:
Fig. 1 is a side view of one form of brake;
Fig. 2 is a section taken along the line II-II of
Fig. l;
Fig. 3 is a section taken along the line III-III
of Fig. 2;
Fig. 4 is a side view of one form a threaded part
of an adjustable length strut employed in the brake; and
Fig. 5 is a side view of a modified form of a
threaded part of an adjustable length strut employed in
the brake.
An internal shoe drum brake shown in Fig. 1 comprises
a pair of opposed arcuate brake shoes 10 and 12 having
one pair of adjacent ends engaging an abutment 14 and
the other pair engaging an actuator 16 for service brake
operation. Two shoe return springs 18 and 20 bias the ~ ;~
shoes 10 and 12 toward each other and away from a brake
drum 22. Numeral 24 indicates a back plate on which the
abutment 14 and the actuator 16 are mounted. Reference
numerals lOa and 12a indicate shoe linings adhered to
the brake shoes 10 and 12, respectively.
As can be seen in Figs. 2 and 3, a hand brake cable
26 is connected to one arm of an operating lever 28.whic~
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The other arm of the operating lever 28 carries or has
fixedly mounted thereto a transverse supporting pin 32
and it has a nose 34 positioned for operative engagement
with the brake shoe 10 and a shoulder 36. A threaded
part 38 of an adjustable strut 40 is pivotally mounted
on the supporting pin 32 and received in a tubular part
42 of the adjustable strut 40. The tubular part 42 has
one end in operative engagement with the brake shoe 12
and other end 44 through which the threaded part 38 extends
into the tubular part 42. Rotatably mounted on the
threaded part is a nut 46 having a ratchet teeth around
its circumference, rotation of the nut 46 varying the
length of the strut 4G. The threaded part 38 of the :
strut 40 engages a pawl arm 48 which is mounted on the
supporting pin 32. The pawl arm has a pawl 50 at one
one end thereof cooperating with the ratchet teeth. As .:.
best seen in Fig. 3, the pawl arm 48 is biased upwardly -: ;
as viewed in this figure toward the operating lever 28 ~:
by means of a coil compression spring 52 acting between
a flange 54 at one end of the supporting pin 32 and the
pawl arm 48 so that the pawl 50 is yieldably held in
engagement with the ratchet teeth of the nut 46. The
coil compression spring 52 is mounted around the supporting
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pin 32 one end of which is anchored to the flange 54 and
the other end of which rests on the other end of the pawl
arm 48 and the shoulder 36 of the operating lever 28 so
as to bias the pawl arm 48 in clockwise direction, as
viewed in Fig. 2 about the supporting pin 32 toward a
predetermined angular position, as illustrated in Fig. 2,
relative to the supporting pin 32.
As can be seen in Figs. 2 through 4, the threaded
part 38 is formed with a stop 56 which limits movement
of the ratchet wheel 46 to define the minimum strut length.
The stop 56 takes the form of a flange or it may take the
form of two diverging projections 56' as shown in Fig. 5.
The threaded part shown in Fig. 5 is substantiaily the
same as the threaded part 38 and is indicated at 38'.
When mounting an assembly comprising two brake shoes
10, 12 having one pair of adjacent ends engaging the
abutment 14 and the other pair engaging the actuator 16,
two shoe return springs 18, 20 biasing the two brake shoes
toward each other and the adjustable strut 40 within the
drum 22, turn the nut 46 until it abuts on the stop 46
to let the strut 40 take the minimum length thereby
setting the maximum diametral distance between the two
brake shoes 10 and 12 at such a length that when the
assembly is mounted within the drum 22 a clearance between
each of the shoe linings on the brake shoes 10, 12 and
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10~5'775
the drum 22 exceeds a~ appropriate amount by 2 to 3 mm. When
the assembly is under this condition, two opposed pistons 16a,
16b of the actuator 16 have their inward ends spaced from each
other to apply the biasing force due to the two return springs
18, 20 across the tubular part 42 and the threaded part 38 to
let the nut 46 to engage the annular end 44 of the tubular part
42.
After mounting the assembly within the drum 22, an
initial adjustment of the clearance can be effected by
operating the handbrake. In the operation of the han~brake,
the operating lever 28 is rotated clockwise, as viewed in
Fig. 2, this movement via the strut 40 urges the brake shoes
10 and 12 against the bias of the springs 18 and 20 toward the
drum 22 and the pawl arm 48 rotates clockwise about the shaft
32 under the action of the spring 52. The nut 46 can be
rotated by the pawl 50 to adjust the length of the strut 40
until the clearance reduces to the appropriate amount. Upon
release of the handbrake the brake shoes are pulled towards
each other by the return springs 18. As the nut 46 firmly
engages the annular end 44 of the tubular part under the action
of the springs 18, 20 upon release of the handbrake, the
resistance to rotation of the nut 46 is great enough, so that
the pawl -
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10f~5775
arm 48 cannot rotate the nut 46 in the opposite direction
and can pick up a fresh ratchet tooth.
It will be seen that upon each operation of the
handbrake the nut 46 can be rotated by the pawl 50 to
adjust the length of the strut if the wear of the brake
is sufficient and the pawl arm 48 picks up a fresh ratchet
tooth.
In operation of the service brake, the actuator 16
forces the brake shoes 10 and 12 apart against the bias
of the shoe return springs 18, 20. Upon release of the
actuator 16 the brake shoes are pulled towards each other
by the return springs 18, 20. It will be seen that the
nose 34 of the operating lever 28 is disposed in a slot
58 formed in the web portion of the brake shoe 10 and
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~E the ~o~ 34 is sized to provide a ~t motion connection
between the operating lever 28 and the brake shoe 10 when
the actuator 16 forces the brake shoes 10, 12 apart from
each other and the brake shoes are pulled toward each
other upon release of the actuator 16.
It will be recognized from the preceding description
that since the initial adjustment of clearance can be ~ ;
effected by operating the handbrake, the brake according
to the present invention is easy to assemble.
